Metal Oxide Varistor with Built-In Alloy-Type Thermal Fuse

ABSTRACT

A varistor with an alloy-type thermal fuse includes a varistor, an alloy-type thermal fuse and a closed cavity. The varistor and the alloy-type thermal fuse are placed in the closed cavity with one surface of the varistor being close to one surface of the alloy-type thermal fuse. The leads of the varistor and the alloy-type thermal fuse extend outside of the closed cavity. The closed cavity is filled with an alloy flux.

TECHNICAL SCOPE

The invention relates to a varistor built-in an alloy-type thermal fuse with protection function of thermal failure, which is particularly applied to zinc oxide varistors and used for the over-voltage protection.

BACKGROUND OF THE INVENTION

The Varistor is abroadly used as over-voltage protection components and surge absorption components of circuitries, equipments and components because of its non-linear volt-ampere character. No matter varistor being used in power circuitries or electrical circuitries, if transient over-voltage happens frequently, the varistor will operate to suppress over-voltage frequently. At the same time, it will adsorb and release surge energy to protect electric equipments and components, which will certainly cause the varistor to failure or damage. When the varistor suffer transient over-voltage, it will be rapid to be destroyed partly or catch fire. Nowaday, most of varistors with thermally failure protected have some disadvantages as following: Some have a complex structure and slower response rate, such as thermally protected metal oxide varistor which is traditionary modules with thermal cutoff device of spring mode and is disclosed by Chinese patent number CN02222055.0; Another type is thermally protected device with a slow response rate or a weak capacity to withstand capacity of high surge current, such as traditional safe varistor is connected with pellet-type or alloy-type thermal fuse exteriorly and is disclosed by Chinese patent number CN00237913.9.

THE CONTENT OF THE INVENTION

The objective of the invention is to provide a varistor with built-in alloy-type thermal fuse which has simple compact structure, rapid response and widely application.

The principle of the invention is to incorporate varistor and temperature fuse to form a varistor with self-invalidation protection utilizing the advantage of alloy-type temperature fuse.

The invention can be completed as following: It comprises a varistor, an alloy-type thermal fuse and a closed cavity; The varistor and alloy-type thermal fuse is placed in the closed cavity with one surface of the varistor being close to one surface of the alloy-type thermal fuse. Their leads are extended to the outside of the closed cavity which is filled with the alloy flux.

The related cavity is including the case with the opening. The varistor and alloy-type thermal fuse are placed in the case in parallel and filled with alloy flux. The upward opening of the case is filled in seal material of epoxy resin to form closed cavity.

The invention also can be completed as following: It comprises varistor, alloy-type thermal fuse and closed cavity. The varistor and alloy-type thermal fuse are placed in the closed cavity in parallel with one surface clinging to each other. Their leads are extended to the outside of the cavity which is filled with the flux resin.

The related closed cavity comprises a case with an opening. The front wall of the case is extended to the outside to form a raised part for accommodating the small case; The opening of the shell is sealed up by seal materials of epoxy resin to form the closed cavity.

The related alloy-type thermal fuse is low melting point alloy wire with leads in its two ends.

The related small case is made in ceramic or material of high conductivity and insulation. At least one side wall should be smooth. Firstly, located thermal fuse in the small case which is made in ceramic or other material of high conductivity and insulation. This method can save the material of flux resin and prevent from dispersal. Also it can extinguish arc and at the same time improve the performance of insulation.

We can make products with different structures according to the requirements of the circuits on the basis of the above basic structure:

Thermally Protected Varistors with Two Leads:

One lead of the alloy-type thermal fuse is connected with one lead of the closer varistor and the connecting point being sealed in the cavity. Another lead of the alloy-type thermal fuse and another lead of the varistor are both extended to the outside of the closed cavity.

Thermally Protected Varistors with Three Leads:

Both leads of the varistor are extended to the outside of the cavity. One lead of the varistor which is close to thermal fuse is connected with one lead of the alloy-type thermal fuse and the connecting point is sealed in the cavity. Another lead of the alloy-type thermal fuse is extended to the outside of the cavity.

Thermally Protected Varistors with Four Leads:

The leads of the alloy-type thermal fuse and the leads of the varistor are all extended to the outside of the cavity. Each lead is not connecting with each other.

Thermally Protected Varistors Connected in Series:

Two varistors is mounted in the cavity. Two leads of the alloy-type thermal fuse which is sandwiched between two varistors are respectively connected with one lead of two corresponding varistors. The connecting points are sealed in the cavity. Two varistors are connected in series through thermal fuse. Their another leads are respectively extended to the outside of the closed cavity.

Thermally Protected Varistors in Parallel Connection:

Two varistors is mounted in the cavity. After the opposite leads are connected with each other, then connecting with one lead of the alloy-type thermal fuse, the connecting point being sealed in the cavity. Two varistors are connected parallelly each other. The alloy-type thermal fuse is sandwiched between two varistors. Another two leads of two varistors and another lead (or two leads) of the alloy-type thermal fuse are respectively extended to the outside of closed cavity.

Thermally Protected Varistor with Alarm Function:

Alarm contacts with temperature controlled can be placed at one side of the alloy-type thermal fuse and the varistor in the closed cavity. There are two modes: from normal close contacts turning to normal open conducts or from normal open contacts turning to normal close contacts.

Thermally Protected Varistor with the Function of Startup and Backup Varistor:

Transferable contacts with temperature control which is from normal open turning to normal close can be placed at the side of the varistor. The backup varistor and transferable contacts are linked in the circuit after connecting in series. When transferable contacts turn to normal close from normal open, backup varistor can be connected with circuit and start its function immediately. It is also possible to make a backup varistor with the function which can start the next backup varistor.

In the invention, the varistor and the thermal fuse are integrated, so that the speed of heat transfer is faster and the installation is convenient when in use. Under the action of flux resin, the melted alloy can be shrinked to two balls rapidly toward two leads. We can choose the alloy of different melting point and sizes to match the varistors of different peak current according to different requirements. We can make different types of varistors. They have widely application.

The invention has many advantages. First of all, the invention can satisfy the requirements of the varistors with different peak current and varistor voltage to absorb the over-voltage of lightning strike and surge voltage; Secondly, when the varistor operates to suppress over-voltage frequently, absorbing and releasing surge energy, which will cause the varistor to be bad or disabled. The various structures can have the function of failure protection when the leakage current of the varistor is lower than 10 milliampere (it also can start the function of failure protection when the leakage current of the varistor is lower, but it will reduce the peak current properly. Thirdly, when the varistor withstands transient over-voltage and leakage current of the varistor is lower than 300 milliampere, the various structures of the invention can start the function of invalid protection before the varistor being destroyed. If the leakage current of the varistor is over 10 ampere, the various structures of the invention can start the function of invalidation failure protection rapidly after the varistor being destroyed; Fourthly, the various structures of the invention can promote absorption and release of the surge energy.

BRIEF EXPLANATION FOR ATTACHED DRAWINGS

Picture 1A: The drawing before thermal fuse cutting off;

Picture 2A: The drawing of the basic structure 1;

Picture 2B: The drawing of the basic structure 2;

Picture 3B: The circuit drawing of application for two leads;

Picture 4A: The structure drawing of application for three leads;

Picture 4B: The circuit drawing of application for three leads

Picture 5: The structure drawing of application for four leads

Picture 6A: The structure drawing of application for varistor in series

Picture 6B: The circuit drawing of application for varistor in series

Picture 7A: The structure drawing of application for varistor in parallel connection

Picture 7B: The circuit drawing of application for varistor in parallel connection

Picture 8A: The structure drawing of application with alarm function

Picture 8B: The circuit drawing of application with alarm function

Picture 9: The circuit drawing of application with startup and backup varistor

Remark: 1. case 2. varistor 3. leads of varistor 4 alloy-type thermal fuse 5. leads of thermal fuse 6. seal material of epoxy resin 7. alloy flux 8 small case 9. alarm contacts with temperature controlled and normal open turning to normal close or normal close turning to normal open 10. transferable device with normal open turning to normal close.

Application Methods in Details:

Application One:

As shown in picture 2A, the drawing of the basic structure 1 comprises a case 1, a varistor 2 and an alloy-type temperature fuse 4; The varistor 2 and alloy-type thermal fuse 4 are placed in the case 1 with the surface of the varistor 2 being close to the surface of the alloy-type thermal fuse 4; the case 1 is filled with alloy flux 7, the opening of the shell 1 being sealed up by seal materials of epoxy resin 6 to form the closed chamber, The leads 3 of the varistor and leads 5 of the fuse is placed to the outside of the case 1.

In using, when the varistor 2 is heated caused by various of factors, the heat can-be transferred to ambient alloy fuse 7 by surface first and then transferred to alloy-type thermal fuse until alloy is melted after heating and shrink toward to two leads 5 of the fuse rapidly under the function of alloy flux 7 (as shown in pictures. 1A and 1B), so that switching off circuit. The worsen varistor 2 will be divorced from the circuit.

Application 2:

As shown in picture. 2B, the drawing of the basic structure 2 comprises a varistor 2, an alloy-type thermal fuse 4, a case 1 and a small case 8; The alloy-type thermal fuse 4 and flux resin 7 are placed in the small case 8 which is made by ceramics or other materials of high heat conduction and high insulation, the opening of the small shell 8 being sealed up by seal materials of epoxy resin 6 with the inner side of the small case 8 clinging to one surface of the varistor 2, the small case 8 and the varistor 2 is placed in the case 1 with the opening of the shell 1 being sealed up by seal materials of epoxy resin 6 to form the closed cavity.

When varistor 2 is heated caused by various of factors, Heat can be transferred to ambient alloy flux 7 by surface, then transferred to alloy-type thermal fuse 4) thought it until alloy are melted after heating and shrink toward to two leads (5) of thermal fuse rapidly under the function of alloy flux (7), so that cutting off the circuit. The worsen varistor (2) will be divorced from circuit.

Application 3:

As shown in picture 3A and 3B, the drawing of application for two leads comprises a varistor 2, an alloy-type thermal fuse 4, a case 1 and a small case 8; The front wall of the case 1 is extended to the outside to form a raised part for accommodating the small case; The alloy-type thermal fuse 4 and flux resin 7 is placed in the small case 8 which is made by ceramics or other materials of high heat and high insulation. The opening of the small case 8 is sealed up by seal materials of epoxy resin 6 with the inner side of the small case 8 clinging to one surface of the varistor 2. The small case 8 and the varistor 2 is placed in the case 1 (as shown in picture. 2B); The first lead 3 a of the varistor 2 is connected with the second lead 5 a of the alloy-type temperature fuse 4 and closed in the case; The second lead 3 bof the varistor 2 and the first lead 5 b of the alloy-type thermal fuse 4 is respectively extended to the outside of the case; The opening of the shell 1 is sealed up by the materials of epoxy resin 6 to form the closed cavity.

Application 4:

As shown in picture 4A and 4B, it is the drawing of application for three leads. The difference from application 3 is that two leads 3 a and 3 b of varistor are extended to the outside of cavity. Its one lead 3 a is connected with one lead 5 a of alloy-type thermal fuse 4. The connecting point are sealed in the case. The another lead 5 b of alloy-type thermal fuse 4 are extended to the outside of case. The opening of case 1 is sealed up by seal material of epoxy resin 6.

Application 5:

As shown in picture 5A and 5B, it is the drawing of application for four leads. The difference from application 3 is that the leads 3 a and 3 b of the varistor 2 and the leads 5 a and 5 b of the alloy-type temperature fuse 4 are all extended to the outside of the case. Each lead is not connected with each other; The opening of the case 1 is sealed up by seal materials of epoxy resin 6.

Application 6:

As shown in picture 6A and 6B, the drawing of application for two varistors in series comprises two varistors 2 and varistor 2′, an alloy-type thermal fuse 4, a case 1 and a small case 8. The case 1 Is rectangle. Alloy-type thermal fuse 4 and flux resin 7 are installed into small case 8 whose opening is sealed up by seal material of epoxy resin 6. The case 8 is sandwiched between varistors 2 and varistor 2′. One side ektexine of the small case 8 clings to one surface of the first varistor 2. Another side ektexine of the case clings to one surface of the second varistor 2′. They are placed into the case 1; One lead 5 a of the alloy-type thermal fuse 4 is connected with one lead 3 a of the first varistor 2. Another lead 5 b of the alloy-type thermal fuse 4 is connected with one lead 3 a′ of the second varistor 2′. They are closed in the case 1. The first varistor 2 and the second varistor 2′ are connected in series. Another lead 3 b of the first varistor 2 and another lead 3 b′ of the second varistor 2′ are respectively extended to the outside of the case. The opening of the case is sealed up by seal materials of epoxy resin 6. This application can realize the addition of two varistor voltage. When single varistor is difficult to meet the demand of higher varistor voltage, it will be endured by two varistors with lower varistor voltage and at the same time it has protection function of invalidation.

Application 7:

As shown in picture 7A and 7B is the structure drawing of application for two varistors in parallel connection comprises two varistors 2 and 2′, an alloy-type temperature fuse 4, a case 1 and a small case 8, the difference from the application 6 is: one lead 3 a of the first varistor 2 connecting with one lead 3 a′ of the second varistor 2′ then connecting with one lead 5 a of the alloy-type thermal fuse 4 which is sandwiched between two varistors 2, 2′, the two varistor being connected in series; Another lead 3 b of the first varistor 2 and another lead 3 b′ of the second varistor 2′ and another lead 5 b of the alloy-type thermal fuse 4 are respectively extended to the outside of the case. The opening of the case 1 is sealed up by seal materials of epoxy resin 6. This application can increase peak current when varistor voltage is stable and at the same time it has protection function of invalidation.

According to the theory of application 5 and 6, it is possible to make more than two varistors in series or parallel connection and so on.

Application 8:

Picture 8 is the drawing of application with arm function, based on the structure of application 2 to application 7, it is possible to place alarm contacts with temperature controlled 9 at one side of the alloy-type thermal fuse in the cavity. There are two modes: from normal close contacts turning to normal open conducts or from normal open contacts turning to normal close contacts. The alarm contacts 9 can control the connected indication light to be on or off to realize the alarm function.

As shown in picture 8, the structure drawing of the single varistor with alarm function comprises a varistor 2, an alloy-type temperature fuse 4, a case 1, small cases 8 and 8′; The front wall and the rear wall of the case 1 is extended to the outside to form raised parts 11 and 12 for accommodating the small cases 8 and 8′. The alloy-type thermal fuse 4 and alloy flux 7 are installed into the small case 8 whose opening is sealed up by seal material of epoxy resin 6. The alarm contacts with temperature controlled are installed into another small case 8′. The inner side of the small case 8 clinging to the surface of the varistor 2, the inner side of another small case 8′ clinging to another surface of the varistor 2, the two small cases 8 and 8′ and the varistor 2 are all placed into the case 1 whose opening is sealed up by seal materials of epoxy resin 6.

Application 9:

As shown in picture 9, It is the circuit drawing of application with startup and backup varistor. Based on the structure of application 2 to application 7, it is possible to place alarm contacts with temperature controlled 10 which is from normal open turning to normal close at one side of the alloy-type thermal fuse in the cavity. The device 10 can have parallel connection in circuitry after connecting with backup varistor in series.(As the structure of application 1 to 8). When the temperature of varistor 2 is up to appointed temperature. The second varistor will start its function and realize multilevel backup varistor. The application 7 and 8 can be operated at the same time.

Application 3 to 8, When varistor 2 is heated caused by various of factors, Heat can be transferred to ceramic or other small cavity which is made in material of good conductivity and insulation and it is also possible to transfer to alloy-type thermal fuse 4 and alloy flux 7 through its leads until alloy are melted after heating and shrink toward to two leads of thermal fuse 5 rapidly under the function of alloy flux 7 (as picture 2), so that cutting off the circuit. The upcoming worsen varistor 2 will be divorced from circuit. This design has quick respond for heat. And it has easy and compact structure.

Application 1 to 7, It is possible to solder the leads 3 a and 3 b on silver layer of bare disc of sintered varistor on two sides. The finished products which is sealed by the powder of epoxy resin is placed to the closed cavity and match with alloy-type thermal fuse 4. Another method is to solder one round sheet copper on one-side silver layer of bare disc of sintered varistor, then soldering lead 3 b on round sheet copper. Another silver layer can be as lead 3 a and is placed into the cavity after connecting with alloy-type thermal fuse 5 a. The opening of inside cavity and other spacing parts are filled and sealed by epoxy resin.

INDUSTRY PRACTICABILITY

The invention of a varistor with an alloy-type thermal fuse having a simple structure, connecting easily with other parts, can be volume-produced and have a favorable industry practicability. 

1. A varistor with an alloy-type thermal fuse, comprising: a varistor; an alloy-type thermal fuse; and a closed cavity; wherein the varistor and the alloy-type thermal fuse are paratactically placed in the closed cavity with one surface of the varistor being close to one surface of the alloy-type thermal fuse with leads of the varistor and the alloy-type thermal fuse extending outside of the closed cavity; which is filled with an alloy flux.
 2. The varistor according to claim 1, wherein said closed cavity comprises a case with an opening, the varistor and the alloy-type thermal fuse are paratactically placed in the case which is filled with the alloy flux and the opening of the case is sealed by epoxy resin to form the closed cavity.
 3. The varistor according to claim 1, wherein said alloy-type thermal fuse is a low melting point alloy fuse with leads in its two ends.
 4. A varistor with an alloy-type thermal fuse, comprising: a varistor; an alloy-type thermal fuse; and a closed cavity; wherein the alloy-type thermal fuse is placed in a small case, the small case and the varistor are paratactically placed in the closed cavity, one inner side of the small case being close to one surface of the varistor, with leads of the varistor and the alloy-type thermal fuse extending outside of the enclosed cavity, and wherein the small case is filled with an alloy flux.
 5. The varistor according to claim 4, wherein said closed cavity comprises a case with an opening, a front wall of the case extending outside to form a raised part for accommodating the small case and the opening of the case is sealed by epoxy resin to form the closed cavity.
 6. The varistor according to claim 4, wherein said alloy-type thermal fuse is a low melting point alloy fuse with leads in its two ends.
 7. The varistor according to claim 4, wherein said small case is made of ceramics or other materials of high heat conduction and high insulation with at least one side being smooth.
 8. The varistor according to claim 4, wherein one said lead of the alloy-type thermal fuse is connected with one said lead of the varistor and enclosed within a case, and wherein another said lead of the alloy-type thermal fuse and another said lead of the varistor extended outside of the case.
 9. The varistor according to claim 4, wherein both said leads of the varistor extend outside of a case with one said lead of the varistor being close to the alloy-type thermal fuse and connecting with one said lead of the alloy-type thermal fuse, the joint being enclosed within the case, and wherein another said lead of the alloy-type thermal fuse extends outside of the case.
 10. The varistor according to claim 4, wherein said leads of the alloy-type thermal fuse and said leads of the varistor all extend outside of the case with each lead not connected with the other.
 11. The varistor according to claim 4, comprising a second varistor connected in series with the first, wherein the small case with the alloy-type thermal fuse is sandwiched between the two varistors, one inner side of the small case clinging to one surface of the first varistor, another inner side of the small case clinging to one surface of the second varistor, and wherein the small case is placed in the closed cavity, one said lead of the alloy-type thermal fuse connecting with one said lead of the first varistor, another lead of the alloy-type thermal fuse connecting with one said lead of the second varistor with both enclosed within a case, and wherein another said lead of the first varistor and another said lead of the second varistor extend outside of the case.
 12. The varistor according to claim 4, comprising a second varistor connected in series with the first, wherein the small case with the alloy-type thermal fuse is sandwiched between two varistors, one inner side of the small case clinging to one surface of the first varistor, another inner side of the small case clinging to one surface of the second varistor, and wherein the small case is placed in the closed cavity, one said lead of the first varistor connecting with one said lead of the second varistor then connecting with one said lead of the alloy-type thermal fuse, and wherein another said lead of the first varistor, another said lead of the second varistor and another said lead of the alloy-type thermal fuse all extend outside of a case.
 13. The varistor according to claim 4, wherein temperature controlled alarm contacts are placed at one side of the alloy-type thermal fuse in a case, comprising the modes of normally closed turning to normally opened and normally open turning to normally closed.
 14. The varistor according to claim 4, comprising: a varistor; an alloy-type thermal fuse,; a case; and two small cases, wherein a front wall and a rear wall of the case extend outside to form raised parts for accommodating the two small cases, the alloy-type thermal fuse and the alloy flux are placed in one said small case whose opening is sealed by epoxy resin, and wherein a temperature controlled alarm contact is placed in another said small case, and wherein inner sides of the two small cases respectively cling to two surfaces of the varistor, the two small cases and the varistor are all placed in the case whose opening is sealed up by epoxy resin. 